This disclosure relates to a gas turbine engine having an integrally bladed rotor.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
The fan, turbine and compressor sections of gas turbine engines include one or more circumferentially extending rows or stages of rotatable blades. The rotor blades are connected to and extend radially outwardly from a rotor. During operation the centrifugal loads of the rotor blades must be carried by the rotor within acceptable stress limits.
Conventional rotor blades are carried in the rotor disk by a dovetail or fir tree root which slides into and interlocks with a corresponding dovetail slot in the perimeter of the rotor. However, as the number of blades around the perimeter of the disk increases, there may be insufficient material available for supporting the blades within acceptable stress limits. Accordingly, integrally bladed disks have been developed and are commercially used. Integrally bladed disks do not utilize the interlocked dovetail design but instead are integrally joined to the rotor blades as a single-piece, unitary assembly by milling, forging, casting or other known manufacturing operations. Integrally bladed rotors, or IBRs, can be used to increase aerodynamic efficiency of gas turbine engine while reducing the stresses associated with supporting the blades.
One of the stresses associated with supporting the blades is a hoop stress. The hoop stress is defined as a load measured in the direction of the circumference of a rotating body, the load being created by thermal gradients and centrifugal forces acting in a radial direction. The hoop stress is particularly acute where the gas turbine engine utilizes integrally bladed rotors. Integrally bladed rotors have been known to develop fractures along their perimeter during operation due to the hoop stress and principal stresses. These fractures necessitate replacement of the integrally bladed rotors to avoid a catastrophic failure.
One or more trenches have been used circumferentially between adjacent blades to reduce the hoop stresses. These trenches have been symmetrical in shape.